v1: add support for raw search fields

[ahornerr]

Hi there!

This is my first contribution to this library and I will say it's quite powerful!

I dug around this morning looking for ways to add arbitrary raw attributes to the search queries and was unable to do so. After further consideration it seems the best way would be to add native X-GM-RAW support to this library!

The specification can be found here https://developers.google.com/gmail/imap/imap-extensions but simply put, we can add a X-GM-RAW attribute to the search query.

I find this necessary to my use case and I believe others may also find it useful. I've added the correct logic and tests.

Thanks!

[codecov[bot]]

Codecov Report

Merging #334 into master will increase coverage by 0.11%. The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master     #334      +/-   ##
==========================================
+ Coverage    73.4%   73.52%   +0.11%     
==========================================
  Files          32       32              
  Lines        3516     3531      +15     
==========================================
+ Hits         2581     2596      +15     
  Misses        642      642              
  Partials      293      293

Impacted Files	Coverage Δ
search.go	64.4% <88.88%> (+2.27%)	:arrow_up:

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[emersion]

Agreed. I really don't want to support GMail's nonstandard flags upstream.

[ahornerr]

@foxcpp @emersion This seems like a reasonable (and more flexible) request. I will make some changes.

[ahornerr]

@emersion @foxcpp I've made some changes to generalize the raw search functionality. Originally I had Raw as a map[string][]interface{} but this made testing and repeatability tricky as Maps in Go are unsorted. By specifying them as an array we can ensure that they're always sorted in the same order. Let me know what you think!

[ahornerr]

Actually I don't think this will work. As is my current approach adds parenthesis around the value which Gmail doesn't interpret as a good command.

UID SEARCH CHARSET UTF-8 ... X-GM-RAW ("filename:docx OR filename:xlsx")
BAD Could not parse command

I'll have to go back to the drawing board with this and correct my issue.

[ahornerr]

I've pushed up a better solution that I'm happy with.